Phosphorylation of cardiac myosin binding protein-C (cMyBP-C) regulates sarcomeric structure, as well as myocardial contractility, and confers cardioprotection. My long-term goal is to define the role(s) of cMyBP-C phosphorylation in contractile function in order to understand the molecular mechanisms that underlie cardioprotection. We recently showed that (1) cMyBP-C is an easily releasable and soluble myofilament, (2) dephosphorylation of cMyBP-C results in its degradation and (3) release into the blood post-myocardial infarction (MI) and (4) its N'-fragments appear within 30 minutes of ischemia-reperfusion injury. In addition, we showed that plasma cMyBP-C levels are significantly increased in animal models and patients with MI. Strikingly, the level of plasma cMyBP-C is significantly higher than the gold standard plasma cardiac troponin I (2.0-fold molar). However, verification and validation of the precise amount of plasma cMyBP-C is the next critical step. Therefore, using selective and specific proteomic approaches, the short-term goal is to develop an assay that precisely quantitates the levels of plasma cMyBP-C. My central hypothesis is that cMyBP-C is a bone fide early, selective and measurable cardiac-specific biomarker, which appears within 30 minutes of ischemia. Thus, the overall objectives of the proposal are as follows: determine a cMyBP-C-specific amino acid region in order to develop a selective proteomics-based assay using the liquid chromatography-tandem-mass spectrometry (LC-MS-MS) and selective reaction monitoring (SRM) approaches (Specific Aim 1); verify the accuracy of the SRM approach for quantifying plasma cMyBP-C levels in both animal and human plasma samples (Specific Aim 2); and cross-validate the SRM assay with the conventional sandwich ELISA assay (Specific Aim 3). Plasma samples taken from ischemia- reperfusion-injured mice and patients with MI will be used in these analyses, compared to naive and sham operated mice and normal healthy controls. Validating the proteomic approaches will result in an assay that can accurately measure the level of cMyBP-C in the circulatory system, as well as define its presence as an early-released, cardiac-specific and selective marker of early-onset MI. PUBLIC HEALTH RELEVANCE: This proposal aims to confirm the efficacy of cardiac binding protein-C (cMyBP-C), a sarcomeric cardiac- specific thick filament assembly protein, as an early circulatory biomarker for myocardial infarction. Specifically, the proposed studies will verify and validate cMyBP-C plasma levels through advanced proteomic approaches, leading to the development of diagnostic assays that advance cardiac care.